Posted
by
Unknown Lameron Tuesday January 29, 2013 @01:05AM
from the grow-your-own-sweater dept.

sciencehabit writes "Researchers have identified three genetic mutations that appear to have helped humans survive in the frigid climate of Siberia over the last 25,000 years. One helps the body's fat stores directly produce heat rather than producing chemical energy for muscle movements or brain functions, a process called 'nonshivering thermogenesis.' Another is involved in the contraction of smooth muscle, key to shivering and the constriction of blood vessels to avoid heat loss. And the third is implicated in the metabolism of fats, especially those in meat and dairy products—a staple of the fat-laden diets of Arctic peoples."

Lactase persistence into adulthood is a relatively recent, as you speculated, and is thought to have been introduced approximately 10,000 years ago.

Then AC's comment makes more sense. At first I thought "but how about breast milk? Isn't that also a form of dairy?"

Of course there are differences between milk from various mammals such as cows and humans but the similarities must be great, too. It's quite common to raise say kittens whose mother died using cow's milk.

Lactase nonpersistence is the ancestral state, and lactase persistence only became advantageous after the invention of agriculture, when milk from domesticated animals became available for adults to drink..... http://x.co/sfIC [x.co]

Agriculture is absolutely not required for milk to become available for adults to drink.

Animal husbandry is required and you find that in many nomadic, non agricultural, societies.

It is off topic, but the ability to digest lactose as adults evolved somewhere between 5,000 and 10,000 years ago. The greatest ability to digest lactose as adults is clustered in the Arabian peninsula, southern Iran and Pakistan, far western Africa, and northern Europe (southern Scandinavia, Iceland, Ireland, Great Britain, Denmark, northern Germany, and northern France). I couldn't tell you though if the genetics are the same but it seems unlikely given the geographical clustering.

It is off topic, but the ability to digest lactose as adults evolved somewhere between 5,000 and 10,000 years ago. The greatest ability to digest lactose as adults is clustered in the Arabian peninsula, southern Iran and Pakistan, far western Africa, and northern Europe (southern Scandinavia, Iceland, Ireland, Great Britain, Denmark, northern Germany, and northern France). I couldn't tell you though if the genetics are the same but it seems unlikely given the geographical clustering.

Yes, it is the same mutation you are talking about. The associated mutations (or "snips", SNP -- single nucleotide polymorphisms) are all the same, even in the West African tribes, and are thought to be of a common origin.

However, there actually is a known case convergent evolution of lactase persistence, fully described in this Nature Genetics paper: http://www.nature.com/ng/journal/v39/n1/full/ng1946.html [nature.com] . The authors analysed genotypes of East African pastoral tribes where lactase persistance is also wi

I don't see why--the adaptation allows Eskimo and Inuit (among others) to STORE fat--in large quantities--to allow for the generation of heat directly rather then through the much slower chemical process that the rest of us utilize. While you and I would sit there shivering our asses off, the Eskimo sitting next to you would simply be burning fat reserves, comfortably. I've experienced this exact situation while ice fishing--shivering makes it really hard to bait a hook without including your finger in the deal.

Most Eskimo/Inuit that I've met (I lived in Central Alaska for 10 years) were what most people would call "chubby"--they had a consistent, yet normal layer of fat that could provide them with emergency heating in the event they REALLY needed it. Falling through the ice in the middle of winter would be an example of such an emergency. Otherwise, they carry that fat around all year. Even in summer, fatty foods are a large part of the Eskimo/Inuit diet. But, I'd like to point out that I've never met a truly obese Native Alaskan--I'm guessing because they don't eat all the crap that most other Americans do--it costs too much to ship it there. While most of us would trim fat off of our meat, the fat is the important part of the catch up North. Muktuk (a common Eskimo/Inuit food) is pure whale fat--there is no meat whatsoever.

Interestingly, the Athabaskan peoples traditional range overlaps that of the Eskimo and Inuit where there are no large mountains that block travel between the interior and the coast (like the Brooks Range does). This is interesting because Athabaskan folks are built much different--they tend to be much slimmer in both bone and tissue--yet share many of the same foods and climate. They one thing missing from the Athabaskan diet is marine mammals of the large and fatty variety--whales, seals and walrus. Eskimo and Inuit eat them but the Athabaskans do not really, unless social circles overlap (more of a modern development). Both groups eat salmon, as the rivers from the coast reach far inland where the Athabaskan group historically occupied, and the interior (Athabaskan group) can actually get much colder then the North Slope of Alaska. The three characteristics discussed in this article also exist in most marine mammals.

Perhaps there is some difference to the fat in marine mammals that isn't present in the other main source of fat, namely salmon, and that consuming it led to the adaptation, rather then this being an environmental adaptation? After all, the Athabaskan peoples live in much the same environment, yet are built totally different (ie, do not have large fat reserves).

I find temperatures above 21C unpleasant. In December, I slept a couple nights in -25 temperatures in a -12 rated sleeping bag and was perfectly comfortable. I rarely wear a jacket above 0. I've taken a 45 minute casual swim in 10 water in nothing but shorts and felt a little chilled but fine (though it was sunny).

But I pay for it in the summer. Once it hits 23 my brain slows down. Around 26 it completely shuts off. I've experienced temperatures up to 40, but I'm glad those days are rare.

It's easy for me to overheat. I went on a winter hike in -15 weather and ended up getting moderate hypothermia -- because I left dressed in a "normal" amount of winter wear and sweat my clothing through. I was steaming. Thankfully I had a change of clothes, and two hours in a -7 sleeping bag got me warmed back up to normal.

People think I'm weird for enjoying -30. But I'd much rather have that than 30. I still find it odd that much of the world lives in near-constant 30 and find those high temperatures comfortable.

Right now I'm carrying a fair amount of extra weight, but even when I was trim my temperature preferences were the same (I took the swim at the skinniest point in my adult life when I was buying shirt to fit my chest).

Sounds about right for me as well, thankfully not to quite the same degree as you. I overheat easily, like for instance riding my bicycle even in winter weather with just a regular jacket on. Forget about bicycling for long distances in summer, even in shorts and a t-shirt, I'm sweating like mad in minutes.

I have a theory that this is related to my inability to get below ~95kg. I work out hard 3-4 times per week (hard ~1 hour crossfit workouts), I always take the stairs, I've all but eliminated white rice,

But if you're living in Siberia you don't really have to worry about hot weather.

No quite true. Siberia during ice age and Siberia today are two different climatic patterns.
Nowadays it is not unheard of to experience up to 40C during spring/summer. So people fit to withstand cold are going to suffer during heat waves.

Some mutations offer no advantage only a disadvantage. Why can't one just be an advantage without a trade-off. It is not like real life is like a Video Game or D&D where there is a goal for balance. Sometimes things are just better or worse than before.

I read a theory once that I found interesting: that arterial plaque is a legacy of survival in an ice age or in an extremely cold environment like Siberia.

Here's how it goes, from memory: Humans get antioxidants from plants, but in extreme conditions plants were less available and humans may not have gotten enough antioxidants. Absent the antioxidants, free radicals posed a greater health risk.

Arterial plaque provided some defense against the deleterious effects of the free radicals, and helped the humans survive the freezing times... long enough to reproduce. Maybe in middle age the hardening of the arteries had deleterious effects of its own, but evolution is all about what helps reproduction, not so much what helps the individual live to a ripe old age.

This sounds sort of plausible but I don't have the background to evaluate it. It could also be one of those "wet streets cause rain" theories that invert cause and effect... is arterial plaque not the body's defense against free radicals but simply damage caused by them?

Of course not only in the mitochondria. Reactive oxygen species are also one of the first lines of defense against bacteria; macrophages generate reactive oxygen in the phagosomes - when macrophages ingest a live bacterium, it then becomes surrounded by a membrane, forming a phagosome. It is best explained with a picture: http://textbookofbacteriology.net/Phago.jpeg [textbookof...iology.net]

Next, the phagosome changes into what is called phagolysosome, which is like a death cage for the bacterium. All sorts of nasty enzymes and mole

If I'm understanding recent findings correctly, free radicals are probably NOT related to aging, and may be a defense mechanism against bacteria.

OTOH, that was an isolated study, so perhaps it's wrong. Still, I'd be hesitant about any certainty right now. (In particular, high levels of anti-oxidants in the blood were associated with shorter life-spans. Of course we're talking mice here.)

They actually might be _both_. ROS are used as cellular poisons by macrophages - that's an old and not a controversial result. Recent findings also show that ROS might help in cancer prevention. But at the same time radicals ARE implicated in normal cell damage - that's also a pretty clear result.

Fun detail: beauty used to be seen in fat, matronly bodies. These embodied wealth which was rare back in the day. We keep finding statues and images which all suggest the same thing all over the world. Fat was beautiful before food became abundant in very recent history.

1. Just like the article says and unlike the Slashdot summary suggests, shiver-free thermogenesis is old and all mammals share it.

2. The researchers found traces of positive selection in a gene involved in shiver-free thermogenesis.

3. How do you look for traces of selection? A mutation in a DNA fragment coding for a protein can have two effects: either it changes the corresponding amino acid in the protein sequence (non-synonymous mutation), or it does not (synonymous mutation). This is because genetic code is redundant and different codons code for same amino acids, so a change from one codon to another does not have to change the protein. Synonymous mutations are assumed to be neutral for evolution (although they are not, not always).

Now, if you look at many possible variants of a gene and collect many different mutations, you can calculate whether the ratio of non-synonymous to synonymous mutations (called the dN/dS ratio) is (i) higher (ii) lower or (iii) quite like expected. Depending on the outcome of the test, you can say:

- if it is higher than expected, then there is a positive selection force at work (the gene is pushed towards change)- if it is lower than expected, then we have a case of purifying selection; the gene is being actively maintained as it is, and any non-synonymous mutations are being removed from the population- if it is neither lower nor higher, the gene is just not important

4. So, nice, you found that a gene related to non-shiver thermogenesis shows traces of positive selection. So what?

The answer is, not much. You do not always know which mutation was the one being selected. And even if you can pinpoint it, very often you will not be able to say what it actually does. So fine, you have a leucine replaced by arginine at position 186 in a protein chain; you might be able even to model the new sequence and see a delicate shift in the structure of the protein. How does it relate to the protein function? What has been modified or improved? No idea.

5. OK, why is that important? It is important because much of the genetic variability of the humans that we know is thought to have been fixated by genetic drift and other neutral evolutionary effects (like surfing the wave of colonization) - rather than selection. There are few examples of selection known. Light skin is one of them, and is thought to be an adaptation to the vitamin D deficiency caused by lack of sun at high latitudes. Mutation that keeps lactase being produced throughout life is another one. There were independent (convergent) events in both cases, by the way.

Look, humans are special. Special in the sense that humans are genetically extremely uniform, and the genetic differences between, say, native Australian, a blond-haired, blue-eyed Swede and a member of the Mbuti people from Africa are all together much smaller than between two chimpanzee individuals from groups living a few hundred kilometers apart. And moreover, these few mutations specific for some people but not for other seem to be more or less neutral in their character.

Finding differences that are *not* neutral, that are actually doing something is therefore an interesting thing. Notably, the few existing differences like that are linked to mundane things like metabolism or immune response (yes, some people are special because they don't fart after drinking milk, how is that for a superior race), and not, for example, to cognitive and brain development. The latter differences are found between humans and other primates.

"gene is not important" -> gene itself might be important, but its precise sequence might not matter because different variants are able to fulfill the same function. The problem is that a synonymous mutation usually is not visible to natural selection, but that doesn't mean that a non-synonymous mutation is always visible; many non-synonymous mutations are effectively ne

"Complex machinery was always universal within a sexually reproducing species. If gene B relied on gene A, then A had to be useful on its own, and rise to near-universality in the gene pool on its own, before B would be useful often enough to confer a fitness advantage. Then once B was universal you would get a variant A* that relied on B, and then C that relied on A* and B, then B* that relied on C, until the whole machine would fall apart if y

You can make precisely the same argument about the last common ancestor between humans and chimps, or the last common ancestor of humans and neandertals. In a general context, chimp brain is as complex as ours. Yet evolution happened in between, we can track it, and we can see that it did in fact modify the cognitive functions of that ancestor; chimps are not humans. And hell, even the developmental machinery that makes an egg develop into an adult vertebrate is complex and interdependent, and if what you are quoting were true, one would expect all vertebrate life remain at the stage of a fish.

The actual reason might be much more mundane: the initial small population of modern humans expanded so rapidly that any resultant genetic differences between populations are the result of neutral evolution (like genetic drift) rather than natural selection. This is also why genetic diversity is inversely correlated with geographic distance to Africa. Essentially, we are all still this same small initial population, but we expanded like a balloon, taking down - directly or indirectly - any other populations that might have existed at times (like the neandertals, denisovians and many, many other hominins).

Your refutation is only valid among populations that continually reproduce with one another. If two populations of primates were geographically separated, and then one evolved into chimps and the other into humans, there would be no issue of cross-mating diluting and neutralizing a complicated trait. Do we know that something like that did not happen?

I might be way off since I don't really understand the subject but is it possible that this difference between a mostly genetic drift and a mostly natural selection races the difference between dominating and being dominated by the environment? This research might end up helping pinpoint when we started using our brains to modify the environment around us?

Not even that. I would rather say: humans with these mutations had a higher chance to leave offspring. It's not like we are talking about a single mutation that is present in all humans native to Siberia, but rather that a frequency of certain genotype is higher in these areas.

... would be for body fur/hair to re-emerge? I wonder why this didn't happen? Ok , obviously they're wearing clothes and had fire but if you're STILL cold even with that assistence then surely having more body hair would help you keep warmer? Yet the asian peoples including those in siberia are LESS hairy than other races. Strange.

would be for body fur/hair to re-emerge? I wonder why this didn't happen? Ok , obviously they're wearing clothes and had fire but if you're STILL cold even with that assistence then surely having more body hair would help you keep warmer?

The advantage of clothes is that you can take them off when you get too hot. Even in Siberia, it can be warm in the daytime, in summer. When dogs lie in the shade panting, we can put on a hat, drink some water from a container, and keep going. My Persian cat has a thick fur coat, and is very comfortable in winter. In summer, it lies on its back on the tiled floor trying to stay cool and I have to get out the clippers.

That's why the whole concept of "Alien" is dumb. A "perfect killing machine". No, a gun

This mutation isn't about keeping them warmer overall, it's about them keeping warmer when they get cold.

If they grew body fur that would keep them a bit warmer all the time, so they'd compensate by wearing fewer clothes or building smaller fires, maybe an advantage from a resource perspective but not a big one (and the extra hair may make the heavy clothes uncomfortable).

But this mutation is more like having a better thermostat, most of the time it doesn't matter, but when you don't have enough clothes or

You can father a child with any female individual from one of these groups and that offspring will be able to breed with any of the people in our world, so on and so forth. Of course there will be genetic variants expressed. That is normal and desirable in any population - we really need more diversity and mixing, not less. As a species we need as much opportunity to recombine genetics in favorable ways as possible (with inevitable unfavorable combos happenin

I dont see that he said anything outlandish to desrve hatred. He simply argued against the position of "races dont exist". He has a point; the races do exist, and they bring with them certain biological differences. And since that's all he said, I think you're overreacting a bit. Let's wait until he actually says something bigoted before crucifying him for it.